1. Field of the Invention
The present invention relates to a vibrating gyroscope and an electronic device using the gyroscope, for example, a vibrating gyroscope for use in a camera-shake correction device provided in a video camera, and other apparatuses using such a gyroscope.
2. Description of the Related Art
For example, Japanese Unexamined Patent Application Publication No. 2001-227953 discloses in FIG. 6 thereof a vibrating gyroscope in which a prismatic vibrator that exhibits bending vibration with two free ends is mounted on one major surface of a mount board while nodes of the vibrator are supported by support members so that the longitudinal direction of the vibrator is parallel to the major surface of the mount board.
In such a known vibrating gyroscope, the vibrator is mounted on one major surface of the mount board such that the nodes of the vibrator are supported by the support members. Electronic components that define a driving circuit and a detection circuit are also mounted on the mount board. After the resonance frequency of the vibrator, the functions of the driving circuit and the detection circuit, and so on are adjusted, a cover is attached to the mount board, thereby completing the vibrating gyroscope.
In the above-described vibrating gyroscope, it is quite difficult to prevent bending vibration of the vibrator, which is caused by excitation of the driving circuit, from propagating to the mount board through the support members. When the vibration of the vibrator propagates to the mount board, the mount board itself sometimes resonates with the vibrator and exhibits bending vibration. Although bending vibration of the mount board is substantially reduced by attaching the cover to the mount board, the cover is attached after the resonance frequency and the functions of the circuits are adjusted in order to simplify the adjustment operation. For this reason, even when the characteristics of the vibrating gyroscope are optimally adjusted in a state in which bending vibration of the mount board is strong before the cover is attached, when bending vibration of the mount board is reduced by attaching the cover, the characteristics deviate from the optimum state.
Bending vibration of the mount board due to resonance caused by the propagation of bending vibration of the vibrator increases as the self-resonance frequency of the mount board is decreased, as shown in FIG. 2. Furthermore, the mount board generates a strong vibration when the self-resonance frequency thereof coincides with the frequency of bending vibration of the vibrator, as similarly shown in FIG. 2.
In general, the self-resonance frequency of the mount board is determined by the material and the size, such as thickness and length, of the mount board. Since the degree of flexibility in designing the material and length of the mount board is often low due to price and size, the self-resonance frequency is optimally determined by the thickness of the mount board in most cases. Since the self-resonance frequency increases as the thickness increases, the thickness is generally selected such that the self-resonance frequency is higher than the vibration frequency of the vibrator.
However, increasing the thickness of the mount board results in an increase in height of the vibrating gyroscope itself, and this does not satisfy recent demands for low-profile electronic devices.
To overcome the problems described above, preferred embodiments of the present invention provide a low-profile vibrating gyroscope having a thin mounting board and which prevents the characteristics from changing when the characteristics are adjusted before a cover is attached to the mount board and when the vibrating gyroscope is completed after the cover is attached.
According to a preferred embodiment of the present invention, a vibrating gyroscope includes a mounting board having a first principal surface and a second principal surface, a vibrator having nodes and mounted on the first principal surface of the mounting board to produce bending vibration with both ends unsupported, support members for supporting the vibrator at the nodes such that the longitudinal direction of the vibrator is substantially parallel to the first principal surface of the mounting board, driving-and-detecting circuit components mounted on the first principal surface of the mounting board, and a cover that is mounted on the mounting board after the vibrator and the driving-and-detecting circuit components are mounted. An original self-resonance frequency of bending vibration of the mounting board itself is lower than the frequency of bending vibration of the vibrator, and a modified self-resonance frequency of bending vibration of the mounting board when the vibrator and the driving-and-detecting circuit components but not the cover are not mounted thereon is higher than the original self-resonance frequency of bending vibration of the mounting board itself, and does not coincide with the frequency of bending vibration of the vibrator.
Preferably, the modified self-resonance frequency of bending vibration of the mounting board is higher than the frequency of bending vibration of the vibrator.
Preferably, at least one of the driving-and-detecting circuit components is mounted so as to cross over an antinode center line of bending vibration of the mounting board due to resonance. Furthermore, preferably, the driving-and-detecting circuit component mounted to cross over the antinode center line of bending vibration of the mounting board is a bare chip IC.
In the vibrating gyroscope having such features, vibration of the mounting board is effectively suppressed, and the characteristics of the vibrating gyroscope are prevented from deviating from the optimum state when the cover is attached. Moreover, the characteristics of the vibrating gyroscope do not substantially differ when the characteristics are adjusted before a cover is attached to the mounting board and when the vibrating gyroscope is completed after the cover is attached, and variations of the characteristics are greatly reduced. In addition, since a thin mounting board is used, a low-profile vibrating gyroscope is achieved.
According to another preferred embodiment of the present invention, an electronic device includes the above-described vibrating gyroscope of other preferred embodiments of the present invention.
Since the electronic device includes the novel vibrating gyroscope, accurate information regarding the angular velocity is consistently obtained and performance is greatly improved.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.